By converting data stream of high-speed transmission to data stream of low-speed parallel transmission, Orthogonal Frequency Division Multiplexing (OFDM) greatly reduces the sensitivity of a system against the frequency selectivity of multipath fading channels. By introducing a cyclic prefix, the OFDM further enhances the capability of the system of resisting intersymbol interference. Furthermore, the features such as a high utilization rate of the bandwidth and simple implementation make the application of the OFDM in the field of wireless communication even wider. A WiMAX system, which is based on Orthogonal Frequency Division Multiple Access (OFDMA), is a system using the OFDM technology.
The advancing wireless communication technology and the changing market demands require that technologies and standards can absorb new technologies through the process of constant evolution and meet new requirements at the same time. Through the process of evolution, standards and systems realized according to the standards not only can continue the life thereof by smooth upgrade and protect the existing resources of subscribers, but also provide more and better services compared with old systems. With the rapid development of communication technologies, mobile WiMAX systems based on IEEE 802.16e (16e for short) air interface standard can not meet the demands on high transmission speed, high throughout, rapid movement and low time delay of wideband mobile communication in the future. At present, the TGm task group of IEEE 802.16 workgroup is committing itself to formulating improved air interface specifications IEEE 802.16m (16m for short), which can support a higher peak rate, spectrum effectiveness and sector capacity.
A 16m system in this document expresses a WiMAX system adopting air interface standard IEEE 802.16m and comprises a backward compatible 16m system (also called a 16m/16e hybrid system) and a non-backward-compatible 16m system (also called a 16m-only system). A base station in the 16m system is called a 16m base station. As defined by the IEEE 802.16m, a downlink sub-frame in the 16m-only system is called a 16m downlink sub-frame and a terminal in the 16m-only system is called a 16m terminal. While a 16e system expresses a WiMAX system adopting air interface standard IEEE 802.16e. As defined by the IEEE 802.16e, a downlink sub-frame in the 16e system is called a 16e downlink sub-frame and a terminal in the 16e system is called a 16e terminal. The backward compatible 16m system comprises both 16m downlink sub-frames and 16e downlink sub-frames and can serve both the 16m terminal and the 16e terminal.
In order to realize the effective application of low delay services in the 16m system, a current design of a 16m frame structure mainly takes a three-layer design concept of super-frame, frame and sub-frame into consideration. FIG. 1 is a diagram of super-frame structure constitution suggested in the current design of a 16m frame structure. The length of a super-frame 101 is 20 ms and consists of 4 frames 102 each with a length of 5 ms, and super-frame control information 103 is located in a plurality of symbols at the start of the super-frame. The frame 102 consists of 8 sub-frames 104, wherein the sub-frames 104 are divided into downlink sub-frames and uplink sub-frames and can be configured according to the system. The sub-frame 104 is composed of 6 OFDM symbols 105. According to the frame structure as shown in FIG. 1, the frame with a length of 5 ms comprises 8 sub-frames.
On the basis of the three-layer frame structure of super-frame, frame and sub-frame, the 16m system also must take backward compatibility with an existing WiMAX terminal into consideration and therefore, it is necessary to think about allocation of 16m sub-frames and 16e sub-frames and reasonable configuration for a frame structure to reduce interference among systems with different configurations.
A super frame header is in a sub-frame at the start of the super-frame. In a backward compatible 16m frame structure, a downlink comprises 16e downlink sub-frames and 16m downlink sub-frames. As different base stations have different 16e and 16m service requirements, in order to enhance the resource utilization rate of the 16e/16m hybrid system, the hybrid ratio of 16e downlink sub-frames to 16m downlink sub-frames may be set different for different base stations, while in the same base station, the hybrid ratio of 16e downlink sub-frames to 16m downlink sub-frames may also vary by taking a super-frame as a minimum periodicity according to the change of services. The description file of the current 16m system defines the relation between a 16e frame and a 16m frame. An offset with a fixed sub-frame length between the 16m frame and the 16e frame is called 16m frame start offset, namely the offset between the starting location of the 16e frame and the starting location of the 16m frame, and the offset takes a sub-frame as its unit, as shown in FIG. 2.
At present, no good solution is available for solving the problems of how to allocate 16e downlink sub-frames and 16m downlink sub-frames in downlink sub-frames of a 16m frame, how to indicate allocation information of the downlink sub-frames and how for a terminal to acquire the allocation scheme.